Field of the Invention
The present invention relates to a technology for controlling a heater included in an image forming apparatus.
Description of the Related Art
In an image forming apparatus having an electrophotographic process, image defects may occur due to, for example, dew condensation caused by environmental fluctuation, such as coldness at night or in the morning depending on the region or season, and a rapid increase in room temperature caused by the use of an air conditioner immediately after the start of work in an office. As a result, in order to prevent dew condensation, there is known a method in which, after the image forming apparatus has been installed, dew condensation is prevented by adding a heater (hereinafter referred to as “environment heater”) configured to maintain temperature at a constant level in the image forming apparatus based on the usage environment. The environment heater is installed in the image forming apparatus based on a determination by a maintenance worker or based on the needs of a user.
In recent years, image forming apparatus have been required to have more stable image quality and longer life. In order to satisfy those requirements, it is necessary to further stabilize, in an electrophotographic process, the temperature of parts around a photosensitive drum and the temperature in a cassette in which recording sheets are stored. However, the environment heater is a type of heater to which a fed AC commercial power supply is directly input. In view of this, in Japanese Patent Application Laid-open No. 2009-216827, there is proposed a configuration in which an input circuit to an AC heater is changed depending on a voltage of the AC commercial power supply, which is different in each intended market region.
In Japanese Patent Application Laid-open No. 2009-216827, there is disclosed an environment heater to be selectively mounted to an apparatus main body depending on the voltage of the AC commercial power supply to be used.
However, in the heater configured to use the AC commercial power supply, the amount of heat generated by the heater is increased as the supplied voltage is increased. Therefore, when the AC voltage supplied to the image forming apparatus varies, the amount of heat generated by the AC heater in accordance therewith also varies.
When the voltage of the commercial power supply varies depending on the region in which the image forming apparatus is installed, the amount of heat generated by the AC heater also varies, and hence it is difficult to maintain the temperature at a constant level using the AC heater. In view of this, there has been proposed usage of a DC heater configured to use DC power obtained by subjecting the AC commercial power supply to alternating current/direct current (AC/DC) conversion. The DC heater is used as the environment heater.
In particular, in an image forming apparatus having a power saving mode, power is also required to be fed to a control unit configured to control the state of the power saving mode. In order to feed power to such a control unit, there is provided a control circuit DC power supply configured to constantly output the power supply voltage.
Therefore, there have been proposed usage of the DC heater as the environment heater as described above, and also the usage of the above-mentioned control circuit DC power supply as a power supply of the environment heater.
However, with the configuration described in Japanese Patent Application Laid-open No. 2009-216827, even though measures are taken for each standard value of the voltage of the AC commercial power supply, there are no measures for dealing with variation in the voltage value. In order to tackle this issue, as the environment heater, a configuration using the DC heater may be used. When a DC power supply having an output voltage that is controlled at a constant voltage is used as the power supply for the DC heater, temperature ripples may be reduced even when there is variation in the voltage of the commercial power supply.
However, as the power supply for the DC heater, when a plurality of environment heaters are connected in parallel to a control circuit power supply configured to operate even during the power saving mode, a timing occurs in which power is simultaneously fed to the plurality of environment heaters, which causes the maximum power consumption of the control circuit power supply to increase. As a result, it is necessary to employ a high-output control circuit power supply. However, in this case, there remains a problem in that the power consumption of the image forming apparatus during the power saving mode is increased.
Further, when the DC heater is simply connected in parallel to the control circuit DC power supply as the environment heater, apart from in the power saving mode in which the environment heater is not driven, the power consumption of the control unit is increased in a standby mode or an image forming mode.
Therefore, as the DC power supply, it is necessary to employ a high-output control circuit DC power supply, which is capable of dealing with an increase in the power consumption of the DC heater, which is added to the power consumption of the control unit. However, in this case, there arises a problem in that power of the image forming apparatus during the power saving mode is increased.
In general, a control circuit DC power supply is a power supply configured to feed power to a logic circuit, typified by a central processing unit (CPU) and an application-specific integrated circuit (ASIC), and a load drive DC power supply is a power supply configured to feed power to loads such as motors and a solenoid. Therefore, the load drive DC power supply has a higher voltage than the control circuit DC power supply. When the voltage applied to the DC heater increases when switching from the control circuit DC power supply to the load drive DC power supply, power increases, which may cause abnormal heating. Further, a deviation (hereinafter referred to as “temperature ripple”) from a target temperature may increase.
It is a primary object of the present invention to provide an image forming apparatus capable of suppressing an increase in power during the power saving mode.
Further, it is also an object of the present invention to perform, in the image forming apparatus, temperature control by arranging a heater, and to suppress abnormal heating and temperature ripples of the heater.